First principle investigations of the Pbnm phase BiFeO3, BiFe0.875Mn0.125O3 and Bi0.875X0.125Fe0.875Mn0.125O3 (XBFM) (X = Ce, Gd, Lu)

The structural, magnetic, electronic and optical properties of Pbnm BiFeO3 (BFO), BiFe0.875Mn0.125O3 (BFM), Bi0.875X0.125Fe0.875Mn0.125O3 (XBFM) (X = Ce, Gd, Lu) have been investigated by the first principles within the PBE+U scheme. It is shown that the dopant Mn in the B sites and Ce (Gd, Lu) in the A sites improves the crystalline quality. The magnetic moments of Bi0.875Ce0.125Fe0.875Mn0.125O3 (CBFM) and Bi0.875Gd0.125Fe0.875Mn0.125O3 (GBFM) are 10 μB and 16 μB which mainly arises from the strongly localized unpaired 4f electrons of Ce and Gd, 3d electrons of Mn and Fe. While, as BFM, the magnetic moment of Bi0.875Lu0.125Fe0.875Mn0.125O3 (LBFM) is 9 μB indicating no effect on the magnetization is made by Lu for its full 4f states. The densities of states of the five systems hint that CBFM is metallic and BFM, GBFM, LBFM are still semiconductors. The metallic properties of CBFM arise from the hybridization between Ce-4f and Mn-3d states which leads the Mn 3d5 states to be split into t2g3 and eg2 lowering the bottom of the conduction band to cross the Fermi level. Furthermore, we also study the optical properties of Pbnm BiFeO3 (BFO), BiFe0.875Mn0.125O3 (BFM), Bi0.875X0.125Fe0.875Mn0.125O3 (XBFM) (X = Ce, Gd, Lu). In this work, the optical properties including the absorption spectrum, loss function, refractive index and reflectivity spectrum are discussed in detail.